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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

GALIANO AND BIACK GLACIERS                               85
to have had shattering in the broad area of the lower Galiano without corresponding breaking in the neighboring Atrevida Glacier. The natives would have known it if there had been a five-mile advance. The only remaining hypothesis is that the Galiano Glacier extends out here for 4 or 5 miles as a broad, lowered, moraine-covered piedmont bulb, the other portion being reduced by ablation, which has automatically checked melting, and that this part of the glacier had been nearly buried by alluvial fan deposits before 1890, forests growing upon the unburied knobs of moraine and upon higher parts of the fan. Later, when Galiano Glacier moved forward, under the impulse derived from ava-lanching during the 1899 earthquakes, the forest on the lower end of the visible bulb was destroyed and the thrust even caused the buried ice to push up through the alluvial fan 4 or 5 miles away, destroying the forest there, causing more rapid melting, and giving rise to the distribution of alluvial fan and moraine patches, with new vegetation, seen in 1905.
Observation here and elsewhere in 1906 and 1909 give to this interpretation a probability which we could hardly dare assign to it in 1906 when it stood as the only known case of such a change due to earthquake almTdng. Now the main facts observed here are duplicated in other cases where the facts are matters of direct observations, not of interpretation alone. The only serious difficulties that occur to us in accepting this explanation are the remarkably quick response, of this glacier and the great extent of piedmont area affected, proportionately more than in other cases. The phenomena seem incapable of any other explanation, however, and we are forced to the conclusion that for some reason this small glacier responded not only quickly, but with such vigor as to affect a great area of stagnant, buried ice. There may, of course, be a very deep ice bulb buried here through which the impulse was communicated with such vigof as to spread far out toward its periphery.
Naturally we have searched carefully in the hope of finding the ice itself in this outer disturbed area; but our search has not been successful. Aside from the changes recorded, however, there is some evidence that the ice still lies beneath the deposits beyond the visible ice bulb. Perhaps the most noteworthy evidence is the great abundance of clear, cold water that oozes from all parts of .the, newly-elevated morainic area. There is no known source for this water, which far exceeds the rainfall, other than buried ice, and we have uniformly found the same condition of abundant cool springs and pools where we have other reasons to suspect the presence of buried ice; but we have not found this condition in localities where buried ice is not suspected on the basis of independent evidence. There are also a few areas where slumping has recently occurred, and there are some cracks in the soil, and numerous boggy places, all of which are common phenomena in places where moraine rests on buried ice. From these evidences alone we would have confidently inferred the existence of buried ice here, even though we had not been forced to this same conclusion by the striking changes between 1890 and 1905.
Granting the existence of a buried, stagnant, ice block here we are led to inquire how it came to be in the condition observed in 1890. First it was doubtless an expanded piedmont bulb, and such a condition it would maintain so long as supply equalled general ablation; but when ablation exceeded supply it would begin to waste away and ablation moraine would cover its surface more and more deeply. The further wastage would then be differential and those parts which had least moraine would be lowered most rapidly. It is a common condition in piedmont ice bulbs to find an area immediately in front of